1. Field of the Invention
The invention relates to a control apparatus for a steering mechanism that is used in a material handling vehicle.
2. Description of Related Art
In recent years, as electric material handling vehicles have become more widely used, electric steering mechanisms have also become widely used. In a steering mechanism for steered wheels to which a large friction force is applied, electric power consumption by an actuator for the steering mechanism is large, and thus, a high load is imposed on an in-vehicle battery (see Japanese Patent Application Publication No. 2000-128005 (JP 2000-128005 A)).
Especially in an electric forklift that is an electric-powered material handling vehicle, a shift operation for switching the direction of movement between the forward direction and the backward direction is often performed with an accelerator pedal kept substantially fully depressed.
In this case, because drive wheels are driven by a drive motor while a steering mechanism is driven by a steering assist motor, a large amount of electricity is consumed. In particular, when a shift operation for switching the direction of movement between the forward direction and the backward direction is performed, inertial force is acting on the vehicle body because the vehicle body is already moving forward or backward. The vehicle is required to change the direction of forward-backward movement or to change the travelling direction, against the inertial force. Therefore, during the shift operation for switching the direction of movement between the forward direction and the backward direction, large amounts of motor drive current and steering assist drive current flow, which requires an especially large amount of electricity.
When electric power consumption temporarily becomes large, load on the in-vehicle battery temporarily becomes high. This causes reduction in electricity that can be supplied to the drive motor and the steering assist motor. This may make it difficult to drive the vehicle forward or backward as intended by an operator.